The invention relates to an instrument for destroying concretions in bodies of living tissue using shock waves generated by arc discharge.
One application is the contact-free comminution of kidney stones.
An instrument for the contact-free comminution of concretions in the body of living tissues by means of shock waves is known from U.S. Pat. No. 3,942,531. It is the property of shock waves to exert pressure and tension on the boundary surfaces between media of different acoustic impedances and to be partially reflected. When passing from a biological tissue to a kidney stone, pressure and tension stresses therefore are exerted respectively at the front and rear sides of the stone which is comminuted thereby. When shock waves are introduced from the outside into the body, the patient's skin also forms such a boundary surface with respect to the surrounding air, and high stresses and reflections do take place at this surface. To prevent injury to the skin, the coupling and decoupling sites of the shock waves must abut a medium with an acoustic wave impedance similar to that of the body.
A known solution is to position the body in a tub with degassed water (Beitraege Zur Urologie, Volume 2, page 64). This makes the instrument very bulky, the positioning of the patient is cumbersome, and the locating of the concretion, for instance by X-rays, furthermore, is rendered more difficult.
German Offenlegungsschrift No. 2,913,251, discloses a means for destroying kidney stones which is directly placed on the kidney after surgical intervention on the patient. Accordingly, the distance between the instrument and the kidney stone is very small, and the significant coupling site is only a few square centimeters. The shock waves are directly coupled into the organ by means of a small pouch of water acting as the coupling path and being of a few millimeters thickness. However, the narrowness of this design makes impossible the simultaneous checking of the centering, proper abutting and occurrence of destruction. The problem of injury-free decoupling of the shock waves from the body--as these shock waves do not pass all of their energy into the stone--is not disclosed in this German Offenlegungsschrift.